1. Field of the Invention
The present invention relates to a WCDMA mobile communication system, and more particularly to a transfer format selecting method for optimizing data transfer.
2. Description of the Related Art
In general, wideband code division multiple access (WCDMA) communication systems can be classified into synchronous systems and asynchronous systems. The asynchronous systems include a Universal Mobile Terrestrial System (“UMTS”). A structure of the UMTS communication system will be described with reference to FIG. 1.
FIG. 1 is a block diagram showing a structure of a general UMTS communication system. Referring to FIG. 1, the UMTS communication system includes a core network (“CN”) 100, a plurality of radio network subsystems (“RNSs”) 110 and 120, and user equipment (“UE”) 130. The RNSs 110 and 120 include a radio network controller (“RNC”) and a plurality of base stations (Node Bs) (“base station”, “Node B” or “cell”). For example, the RNS 110 and the RNC 111 include a plurality of Node Bs 113 and 115. Such RNCs are classified into serving RNCs (“SRNCs”), drift RNCs (“DRNCs”), and controlling RNCs (“CRNCs”) according to the functions of the RNCs. The SRNCs and the DRNCs are classified depending on the functions of the RNCs for UEs. If a certain RNC manages information of a certain UE and transfers data of the UE to the CN, the RNC is the SRNC of the UE. If the data of a certain UE is transferred/received to/from the SRNC via another RNC instead of being directly transferred/received to/from the SRNC, the RNC is the DRNC of the UE. In addition, the CRNC represents an RNC for controlling the Node Bs. For example, as shown in FIG. 1, if the RNC 111 manages the information of a UE 130, the RNC 111 is the SRNC. Also, if the UE 130 transmits/receives data thereof to/from an RNC 112 while the UE 130 is moving, the RNC 112 is the DRNC. In addition, the RNC 111 controlling the Node B 113 is the CRNC of the Node B 113. Layer and channel structures of a UMTS will be described with reference to FIG. 2.
FIG. 2 is a block diagram illustrating the layer structure of a general wideband code division multiple access mobile communication system. First, referring to FIG. 2, a Radio Resource Control (“RRC”) layer 141 transmits a control message for a transport format selection to a Medium Access Control (“MAC”) layer 145. In this case, the RRC layer 141 transmits not only the control message for the transport format selection but also transmits a plurality of control messages for controlling the operation of the MAC layer 145. Further, a Radio Link Control (“RLC”) layer 143 receives a Service Data Unit (SDU) from a higher layer and compares the received service data unit with a Protocol Data Unit (PDU). When the received service data unit is smaller than the protocol data unit, the RLC layer 143 concatenates the received service data unit with other service data units, so as to generate a protocol data unit having a size suitable for the protocol data unit. In contrast, when the received service data unit is larger than the protocol data unit, the RLC layer 143 segments the received service data, so as to generate a protocol data unit having a size suitable for the protocol data unit. Further, the RLC layer 143 transfers the generated protocol data units to the MAC layer 145 through a logical channel.
The UMTS channels can be classified into physical channels, transport channels, and logical channels. The physical channels include downlink channels such as a Physical Downlink Shared Channel (PDSCH), a Dedicated Physical Control Channel (DPCCH), and a Dedicated Physical Data Channel (DPDCH), and uplink channels such as a Dedicated Physical Channel (DPCH). The logical channels can be represented by Dedicated Channels (DCHs) which includes a Dedicated Control Channel (DCCH) and a Dedicated Traffic Channel (DTCH). The transport channels include a Random Access Channel (RACH) and a Common Packet Channel (CPCH).
Meanwhile, the MAC layer 145 receives a Transport Block Set (TBS) from the physical layer (PHY) 147, divides the received transport block set into Transport Blocks (TBs), converts the divided transport blocks into protocol data units, and transfers the protocol data units to the RLC layer 143. Then, the RLC layer 143 converts the received protocol data units into service data units and transfers the service data units to the higher layer. In contrast, the MAC layer 145 receives a protocol data unit from the RLC layer 143, divides the received protocol data unit into transport blocks which are real units transmitted through the transport channel, and transfers the transport blocks to the physical layer 147. The physical layer 147 converts the transport blocks received from the MAC layer 145 into radio frames which are real units transmitted from the physical layer, and transmits the radio frames over the air through a corresponding physical channel.
Primitives are utilized in the data transmission between the layers described above, that is, the RRC layer 141, the RLC layer 143, and the physical layer 147, and buffers for storing data, such as a shared memory, are interposed between the MAC layer 145 and the RLC layer 143 and/or between the MAC layer 145 and the physical layer 147. The RLC layer 143 converts the service data units received from the higher layer into the protocol data units, buffers the protocol data units into a Dedicated Control Channel/Dedicated Transport Channel (DCCH/DTCH) buffer 149, and reports the buffering to the MAC layer 145 through the primitives. Whenever it is necessary to read the protocol data units, the MAC layer 145 reads the protocol data units stored in the DCCH/DTCH buffer 149 and maps them onto the transport channel. When necessary or when the MAC layer 145 receives the primitives from other layers, the MAC layer 145 reads the protocol data units stored in the DCCH/DTCH buffer 149 and maps them onto the transport channel, generates the transport blocks by multiplexing and adding headers of the MAC layer 145 according to the type of the mapped transport channel, and transmits the data to L1 (Layer 1) for the transport channel. Further, the MAC layer 145 buffers the generated transport blocks into the transport channel buffer 151. At a point of time when the transport blocks must be transmitted, the physical layer 147 reads and transmits the transport blocks stored in the transport channel buffer 151.
Transport blocks transmitted through the same single transport channel during one Transmission Time Interval (“TTI”) will be referred to as a “Transport Block Set” (TBS), the number of bits in each transport block of the TBS will be referred to as a “transport block size”, and the number of the transport blocks constituting the TBS will be referred to as “Transport Block Set Size” (TBSS). In this case, a Node B reports the transport block set size to a User Equipment (“UE”), so that the number of bits that are rate-matched in a physical layer of the UE can be estimated. In this case, the rate matching scheme is information indicating how repetition or puncturing has been performed when the physical layer of the UE has repeated or punctured with respect to the UE data. As described above, the UE can simultaneously set a plurality of transport channels corresponding to its transmission characteristics (for example, transport channels capable of providing various error correction functions). Each of the transport channels may be utilized in transmitting the information stream of one radio bearer or in transmitting L2 (Layer 2) and higher layer signaling messages. This mapping and transmitting of the transport channels onto and through the same or different physical channels is implemented by the physical channel mapping operation of the physical channel 147.
The characteristics of the transport channels are determined according to the channel coding scheme employed in the transport channel, such as a convolutional coding scheme, and the Transport Format (TF) or the Transport Format Set (TFS) which defines the processing in the physical layer, such as interleaving and service-specific rate matching. The transport format is a set whose members are data processing schemes of the physical layer for the transport channel, and the transport channel usually defines the coding rate and the channel coding scheme by and in which the data transmitted through the corresponding transport channel have been coded, the size (transport block size) by which the data are divided and transmitted, and the number of transport blocks which can be transmitted during one TTI. The timing of the transport blocks is fixed to the frame timing of the physical layer 147, that is L1 (Layer 1). For example, the transport block is generated at every 10 ms, that is, at every point of time which corresponds to a product obtained by multiplying 10 ms by an integer. Therefore, two different transport channels have different details in relation to the transport channels, which means different transport formats.
The transport format can be divided into two parts including a dynamic part and a semi-static part, as shown in Table 1.
TABLE 1Transport Format typeAttributesDynamicTransport Block sizeTBS sizeSemic-staticTTIError protection schemeType of error protection, turbo code,convolutional code or channel codingCoding rateSize of CRC
As shown in Table 1, the dynamic part includes information related to a transport block size and a transport block set size. The semi-static part includes information of the TTI, size of Cyclic Redundancy Check (CRC), and error protection scheme which includes a coding rate and a channel coding scheme for error protection. As described above, a transport format is assigned to each of the transport channels according to the characteristics of the mapped physical channel. In this case, the Transport Format Set (TFS) is a set whose members are all transport formats which can be assigned to the transport channels, and the Transport Format Indicator (TFI) is an identifier for identifying each element constituting the transport format set, that is, each of the transport formats. The semi-static parts of all of the transport formats are equal to the semi-static parts existing in the transport format set. Further, the transport block size and the transport block set size information contained in the dynamic part are generated corresponding to the bit rate of the transport channel. When the bit rate of the transport channel changes according to channel environments and/or service types, only the transport block set size or both of the transport block set and the transport block set size can be changed. In this case, when the transmission rate of the transport channel is fixed or changes slowly, the transport format is mapped to the transport channel. In contrast, when the transmission rate of the transport channel rapidly changes, the transport format set is mapped to the transport channel.
The Transport Format Combination (TFC) is a combination of the transport formats transmitted to the physical layer 147 through a Coded Composite Transport Channel (CCTrCH) of the UE, which has one transport format for each transport channel, and the Transport Format Combination Set (TFCS) is a set of the TFCs transmitted through the CCTrCH. In this case, the TFCS needs not include all of the TFCs of the corresponding transport channels. Since a plurality of TFCSs are generated, the Transport Format Combination Indicators (TFCIs) are necessary in order to identify the TFCI being currently assigned to the transport channel. Therefore, when a transmitting-side of the communication entity, e.g., a Node B, transmits a transport channel with a TFCI which corresponds and is mapped to the transport channel, a receiving-side of the communication entity, e.g., a UE, can decode and demultiplex the transport channel by analyzing the TFCI of the transport channel.
Since a plurality of transport channels can be time-division-multiplexed through the same physical channel, the UE should be capable of recognizing the transport channel to which the physical channel received at a predetermined point of time pertains. Therefore, the UE provides an indicator to each of the transport channels in order to differentiate and identify the transport channels. This indicator is the Transport Channel Indicator (TCI).
Whenever the RLC layer 143 transmits a data request signal, the RRC layer 141 transmits a control signal for selecting a transport format assigned to the transport channel construction to the MAC layer 145. The RRC layer 141 assigns values of priorities, for example ‘1’ to ‘8’, to a plurality of logical channels, for example 8 logical channels, between the RLC layer 143 and the MAC layer 145, so as to control scheduling of the uplink data. From among the priorities, ‘1’ is a value having the highest priority and ‘8’ is a value having the lowest priority. The selection of TFCs in the UE depends on the priorites assigned to the logical channels by the RRC layer 141. Whenever the RLC layer 143 transmits a data request signal, the MAC layer 145 selects a proper transport format for the data transmission under the control of the RRC layer 141. During the transmission according to the priority, some of the transport blocks from among the transport blocks of each of the logical channels may be blocked and delayed by the data transmission of another logical channel having a higher priority. This blocking of the transport blocks for the data transmission of another logical channel is also implemented under the control of the RRC layer 141, and the priority of the interrupted transport blocks is set to be ‘0’ which is higher than the highest priority ‘1’, so that the data having the priority of ‘0’ can be transmitted prior to any other transport blocks.
When the UE transmit power approaches the maximum transmit power which can be transmitted by the UE, and the internal loop for power control cannot be maintained any more due to a coverage problem, the UE assigns a transport format combination having a bit rate lower than that of the current transport format combination to the transport channel. When a bit rate of a logical channel which transfers data from a CODEC supporting the variable rate operation conflicts with the lower bit rate, the bit rate of the CODEC is changed in order to avoid the confliction. Further, the UE continuously measures whether or not the maximum transmit power of the UE can support the temporarily interrupted transport format combination. As a result of the measurement, when the maximum transmit power of the UE is enough to support the temporarily interrupted transport format combination, transport combinations are assigned to the transport channels in reconsideration of the temporarily interrupted transport format combination.
As described above, the MAC layer 145 performs transport format selection in response only to the data transmission request of the RLC layer 143, has a transport format table including all transport formats which can be assigned for the transport format selection, and searches the transport format table under the control of the RRC layer 141 when data transmission is requested by the RLC layer 143, so as to select a transport format for the corresponding transport channel. However, searching the transport format table which includes transport formats of all cases in order to assign a transport format to one transport channel requires considerable amount of time spent in the transport format selection and may cause an overload due to the time required for the transport format selection.